The present invention relates to an objective lens driving apparatus for use in an optical pick-up which is installed in a light recording and/or reproducing system, and more particularly to an improved objective lens driving apparatus in which the structure of a supporting mechanism, for elastically supporting an objective lens driving portion, is improved so as to perform a precise servo control of an objective lens.
Generally, optical pick-ups for projecting a light beam from a laser, etc. onto the surface of a recording medium and detecting the reflected light beam are installed in players using light recording media such as a laser disc player (LDP), a compact disc player (CDP), a multi-disc player (MDP) for a mageneto-optic disc drive (MODD), and so on. Such optical pick-ups for optical discs are apparatuses for reading out digital information stored on the surfaces of the disc in which the reading method is completed by scanning a disc with a laser beam and reading a binary signal via the reflected beam.
Thus, when using an optical pick-up for an optical disc, in order to read the signals correctly, the focus of the objective lens must be controlled accurately. Accordingly, elastic supporting means is provided in the objective lens driving portion, so that the main body of the driving portion is minutely moved in the horizontal direction for tracking and in the vertical direction for focusing.
As shown in FIG. 1, the conventional objective lens driving apparatus disclosed in U.S. Pat. No. 4,646,283 of Matsushita Electric Industrial Co. (Japan), includes four conductive elastic linear members W1 to W4 for connecting both sides of a main body 1 in the driving portion on which an objective lens L is loaded, to the front plate of a nonconductive fixed block 2, thereby elastically supporting main body 1 of the driving portion in the horizontal and vertical directions. Here, conductive elastic linear members W1 to W4 are of the same size and each have respective elasticities of a predetermined direction. Also, conductive elastic linear members W1-W4 pass through fixed block 2 for support, and at the same time are connected to an external circuit (not shown). That is, the above Matsushita patent teaches a technology of supporting the objective lens driving portion as well as supplying current to coils, using the conductive elastic linear members.
In the objective lens driving apparatus having the above construction, when driving portion main body 1 moves in the vertical direction for focusing, parts of tracing coils Tc, which are wound in driving portion main body 1, depart from the magnetic field. At this time, since differences occur between the electromagnetic forces generated in the tracing coils within the magnetic field and those outside the magnetic field, a rolling force is produced in the driving portion main body. Accordingly, elastic linear members W1-W4 twist due to this rolling force.
Thus, as shown in FIG.2, vertically disposed elastic linear member pairs W1 and W2 and W3 and W4 experience a twisting action, caused by the rolling of driving portion main body 1. For this reason, the light beams via objective lens L are obliquely scanned on a recording medium (not shown), which causes imprecise servo control.
Certain improvements have been proposed in an attempt to prevent driving portion main body 1 (on which objective lens L is loaded) from rolling, which include modifying the structure of tracking coils Tc. However, such modifications lead to a complicated structure, a rise in production cost and greater power consumption.